This invention relates to a workpiece feeding apparatus in a seam welding machine for automating a seam welding operation on a workpiece such as a two-wheeled vehicle fuel tank or the like.
The inventors of the subject matter of this application have previously developed a combination apparatus wherein a workpiece is supported through a chucking means on an operational end of a robot so that the portion of the workpiece to be welded may be fed between a pair of upper and lower electrode rolls provided on a seam welding machine. All the respective arms of the robot and the respective turnable members of a wrist portion thereof are arranged to be controlled to be turned in accordance with respective signals by respective driving sources so that the workpiece may be positively moved along on a teaching locus. However, in this apparatus, a particular inconvenience as described below arises.
Namely, there occurs generally a phenomenon in repeated seam welding operations that the holding position for the workpiece by the two electrode rolls deviates towards the lower electrode roll side due to abrasion of the rolls or the like. Consequently, if the workpiece is driven to be moved as above along on the teaching locus, an undesirable force is generated between the workpiece and the chucking means. It becomes impossible to reliably hold the workpiece between the rolls. An inconvenience of the workpiece coming off from the chucking means or derailing of the electrode rolls from the portion to be welded can result.